ValidReferenceConstraint.php

<?php

namespace Drupal\Core\Entity\Plugin\Validation\Constraint;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\Core\Validation\Attribute\Constraint;
use Symfony\Component\Validator\Attribute\HasNamedArguments;
use Symfony\Component\Validator\Constraint as SymfonyConstraint;

/**
 * Entity Reference valid reference constraint.
 *
 * Verifies that referenced entities are valid.
 */
class ValidReferenceConstraint extends SymfonyConstraint {
  public function __construct(mixed $options = NULL, public $message = 'This entity (%type: %id) cannot be referenced.', public $nonExistingMessage = 'The referenced entity (%type: %id) does not exist.', public $invalidAutocreateMessage = 'This entity (%type: %label) cannot be referenced.', public $nullMessage = 'This value should not be null.', ?array $groups = NULL, mixed $payload = NULL) {
    parent::__construct($options, $groups, $payload);
  }

}